Complete Technical Guide

Types • Differences • Advantages and Disadvantages • Service Life • Maintenance

1. What is Activated Carbon?

Activated carbon is a porous material with extraordinary adsorption capacity. A single gram can have an internal surface area of between 800 and 1,500 m²: the equivalent of several football fields compressed into a tiny volume. This property makes it one of the most effective materials for retaining contaminants in water and air.

The activation process consists of subjecting the raw material (coconut shells, bituminous coal, wood, fruit pits, etc.) to high temperatures in a controlled atmosphere, creating an internal network of micropores, mesopores, and macropores that attract and retain pollutant molecules through physical or chemical adsorption.

 

Activated carbon is widely used in:

• Domestic drinking water filtration systems (under-sink, pitcher, reverse osmosis, whole-house)
• Industrial and municipal water treatment plants
• Air purification (masks, air purifiers)
• Wastewater treatment
• Pharmaceutical, food, and chemical industries

2. Carbon Block (CTO) vs. Granular Carbon (GAC)

Regardless of the raw material from which activated carbon is manufactured, filtration cartridges come in two main formats: compacted block and loose granular form.

2.1 Carbon Block (CTO)

The carbon block cartridge is manufactured by compacting fine activated carbon powder under pressure and temperature, forming a solid cylinder with controlled pore sizes (usually between 0.5 and 10 microns).

Unlike the granular format, all water is forced to pass through the solid mass of the block, with no possibility of taking shortcuts through side channels.

Advantages of Carbon Block:

• Additional mechanical filtration: in addition to adsorbing chemical contaminants, the block retains physical particles (sediments, cysts, certain bacteria) down to 0.5 microns.
• No channeling: being a solid block, water cannot take paths of least resistance, ensuring that the entire volume of water is treated.
• Longer contact time: water flows more slowly through the block, which favors adsorption.
• Lower risk of bacterial proliferation: since there are no spaces with stagnant water between granules, the risk of creating bacterial colonies is considerably lower.
• Greater consistency in filtration quality.

Disadvantages of Carbon Block:

• Higher pressure drop: water requires more force to pass through the solid structure, which can reduce flow rate.
• Faster clogging in waters with high sediment content: suspended solids block surface pores before adsorption capacity is saturated.
• Generally higher cost than granular.
• Cannot be regenerated or cleaned once saturated.

2.2 Granular Activated Carbon (GAC)

The granular carbon cartridge contains activated carbon particles ranging from 0.5 to 2 mm in size, loosely packed within a housing. Water flows between and through the granules.

Advantages of Granular Carbon:

• Lower pressure drop: water flows easily between the granules, better maintaining the system's flow rate.
• Excellent for pre-filtration and chlorine removal in large volumes.
• Lower unit cost.
• In industrial open-bed systems, allows backwashing to extend the service life of the filter media.
• Ideal as a pre-filter before a reverse osmosis membrane.

Disadvantages of Granular Carbon:

• Channeling: water tends to follow paths of least resistance between the granules, leaving areas of the bed without fluid contact.
• No mechanical filtration: does not retain physical particles, only adsorbs dissolved contaminants.
• Bacteriological risk: stagnant water areas between granules can become ideal environments for microbial proliferation.
• Lower contact efficiency compared to block.
  
  

2.3 Comparison Table: CTO vs. GAC

Note: In many advanced systems, both formats are used in series. GAC acts as a pre-filter removing the bulk of chlorine and larger solids, and the CTO block finishes the process with fine filtration and removal of trace contaminants.

3. Types of Activated Carbon by Raw Material

The raw material determines the pore distribution of the activated carbon and, therefore, which types of contaminants it can remove with greater efficiency. Not all carbons are equal: the correct choice depends on water quality and target contaminants.

3.1 Coconut Shell Carbon

This is the most widely used in drinking water filtration, both domestic and industrial. It is produced from calcined coconut shells activated with steam at high temperatures.

Pore structure: Massive predominance of micropores (< 2 nm), giving it a high surface area (1,000–1,500 m²/g). Typical iodine number: 1,000–1,200 mg/g.

• Ideal for: removal of chlorine, chloramines, volatile organic compounds (VOCs), trihalomethanes (THMs), tastes, and odors.
• Advantages: high purity, low dust generation, high mechanical hardness, lower environmental impact.
• Limitations: less effective for large molecules such as tannins or humic acids.

3.2 Bituminous (Mineral) Carbon

Obtained from bituminous coal, selected for its broad and balanced pore structure. It is very common in municipal and industrial water treatment applications.

Pore structure: Balanced mixture of micropores, mesopores (2–50 nm), and macropores (> 50 nm). Iodine number: 800–1,050 mg/g. Abrasion index: 80–90%.

• Ideal for: waters with high organic matter load, color, turbidity, hydrocarbons, phenols, and chlorine removal.
• Advantages: broad adsorption spectrum, capable of capturing molecules of different molecular weights, moderate cost.
• Limitations: higher initial dust generation, lower purity than coconut in some parameters.

3.3 Wood Carbon

Produced from woods such as pine or birch. It has a predominantly large pore structure (macropores), suitable for high molecular weight molecules.

Pore structure: Predominance of macropores. Smaller surface area than coconut or bituminous.

• Ideal for: liquid decolorization, removal of tannins, humic acids, dyes, and large molecular size compounds.
• Advantages: excellent for food and pharmaceutical industry applications where decolorization is required.
• Limitations: low mechanical hardness, lower capacity for VOCs and small compounds, not primary for drinking water.

4. Catalytic Activated Carbon: The Key Difference

Catalytic activated carbon is conventional carbon (generally coconut shell or bituminous) that has undergone a surface modification process during or after activation. This process alters the carbon's surface chemistry, introducing active sites with catalytic capacity.

4.1 Dual Mechanism of Action

Physical adsorption: Like any activated carbon, it retains contaminants through Van der Waals forces.

Chemical catalysis (surface reaction): The active sites on the catalytic carbon surface promote the chemical decomposition of chloramines and hydrogen sulfide (H₂S), transforming them into harmless compounds without simply adsorbing them. This means that the active sites remain free to continue reacting, extending the cartridge's service life.

4.2 What Contaminants Does It Remove Best?

• Chloramines (monochloramine, dichloramine) — its primary and differentiating function
• Free chlorine (superior to standard carbon under equal conditions)
• Hydrogen sulfide (rotten egg smell)
• Volatile organic compounds (VOCs)
• Trihalomethanes (THMs)

4.3 Comparison Table: Standard vs. Catalytic Carbon

5. Cartridge Service Life

The service life of an activated carbon cartridge is not a fixed value: it depends on multiple variables that must be evaluated in each installation. Manufacturer guidelines are estimates based on average conditions and must be adjusted to the reality of each water source.

5.1 Factors Determining Service Life

• Inlet water quality: higher concentration of chlorine, sediments, or organics depletes the cartridge faster.
• Flow rate and filtered volume: higher daily consumption means greater wear. Total filtered volume is the most reliable indicator.
• Water temperature: higher temperatures accelerate saturation.
• Presence of organic matter, turbidity, or sediments: clogs the block by mechanical fouling before chemical capacity is saturated.
• Cartridge format: the block clogs mechanically first; the granular depletes chemically more uniformly.

5.2 Indicative Replacement Ranges

In industrial installations, the replacement criterion is based on periodic analysis of outlet water (residual chlorine, color, TOC — total organic carbon) rather than elapsed time.

6. Signs the Cartridge Needs Changing

Waiting for the cartridge to show signs of failure is the worst strategy, especially in drinking water applications. However, knowing the signs allows for action before compromising the quality of the treated water.

• Return of chlorine or chemical taste or smell in filtered water.
• Earthy or musty odor from filtered water (sign of bacterial colonization in GAC).
• Noticeable reduction in water flow rate (mechanical fouling in the CTO block).
• Change in color of outlet water (increased turbidity or yellowish color).
• Out-of-range results in water analysis (residual chlorine > 0 at outlet, increased TOC).
• Exceeding the maximum volume or time indicated by the manufacturer.

7. Care and Maintenance for Maximum Performance

7.1 Correct Installation (Foundation of Everything)

• Flush the system with water before putting the filter into service: the initial flow will wash away carbon dust and trapped air in the pores. It is recommended to discard the first 5–10 liters.
• Soak the new cartridge in clean water for 10–15 minutes before installing it to remove trapped air and activate the filter media.
• Always install in the correct flow direction indicated by the manufacturer (inlet and outlet clearly identified).
• Check for leaks in the filter housing's gaskets or O-rings.

7.2 Operating Conditions

• Working pressure: maintain within the manufacturer's range (typically 30–125 PSI). Excessive pressures can fracture the CTO block or compact the GAC.
• Temperature: most plastic and carbon cartridges are designed for cold water (max. 40°C / 104°F). For hot water, check the model's specifications.
• Flow rate: do not exceed the specified maximum flow rate. A flow that is too fast reduces contact time and, therefore, adsorption efficiency.
• Presence of oils or greases: activated carbon does not remove oils; if the inlet water contains them, install a coalescing pre-filter before the carbon cartridge.

7.3 Backwashing in Industrial Systems with GAC Bed

In industrial installations with open granular carbon beds in a tank (not in a sealed cartridge), periodic backwashing is the most important maintenance operation.

• Frequency: daily to weekly depending on the solid load in the inlet water.
• Procedure: reverse the water flow through the bed with sufficient flow to expand and fluidize the carbon (30–50% bed expansion), removing accumulated solids and breaking up channeling.
• Duration: 10–20 minutes per cycle until the backwash water runs clear.
• Caution: do not use excessive backwash flow that would wash carbon out of the tank or cause mechanical damage to the granules.

7.4 Storage of Replacement Cartridges

• Store unopened cartridges in their original packaging, in a cool, dry, and dark place.
• Avoid extreme temperatures (freezing or intense heat), which can damage the wrapping or the carbon block.
• Do not use cartridges that have exceeded their storage expiration date (typically 2–3 years unopened).
• Once installed and wetted, the cartridge cannot be stored again without bacterial growth. If the system will be inactive for more than 2–3 weeks, replace the cartridge when reactivating it.

7.5 Filter Housing Cleaning

• Each time the cartridge is changed, clean the inside of the filter housing with a solution of potable water and a small amount of chlorine (1 teaspoon of household hypochlorite per liter of water).
• Rinse thoroughly with clean water before installing the new cartridge.
• Inspect the gasket or O-ring: a deteriorated gasket causes leaks and reduces the effective pressure of the system. Replace it at the first sign of wear.
• Do not use harsh detergents or solvents that could damage the filter housing plastic or be absorbed by the new cartridge.

8. Summary and Selection Guide

Choosing the right activated carbon requires knowing the quality of the inlet water. Ideally, a water analysis that includes free chlorine, chloramines, TOC, turbidity, and conductivity should be performed to design the appropriate filtration system.

This document is for informational and technical purposes. For critical applications in drinking water or industrial processes, consult a specialized water treatment engineer.